The types and concentrations of synthetic chemicals that are in our environment are of greater concern to government, businesses, and society in general than in any time in history. Multiple factors contribute to this heightened concern, such as national security issues related to the use of deadly chemicals as weapons, the risk of an intentional or accidental chemical spill, environmental awareness, and increased understanding of the potential impacts of such chemicals on human health. The range of applications for sensors that can accurately measure volatile gases is wide.
For example, the Department of Homeland Security needs sensors to detect the presence of chemical weapons, such as chemical warfare agents and explosives. These sensors can be integrated into traffic lights in large cities, as components of air-intake valves in municipal buildings, and used as on-board devices for unmanned aerial vehicles or robotic vehicles that are used to explore hazardous situations. Similar sensors can be used to detect natural gas leaks for home and business owners and to monitor outdoor air in local communities, school playgrounds, or agricultural settings.
Approximately 70,000 illnesses and deaths occur annually as a result of occupational exposure to toxic gases, at a cost of more than $100 billion from lost wages and medical expenses. Millions of US workers in various industries are exposed to vapors from various organic chemicals that are recognized by the National Institute of Occupational Safety and Hygiene (NIOSH) as carcinogens, reproductive hazards, and/or neurotoxins. As such, industrial manufacturers need sensors to monitor facility air during production, survey product off-gassing, and assist with maintaining safe levels of permissible exposure limits (PELs) to protect workers against the health effects of exposure to hazardous substances including toxic industrial chemicals. NIOSH and other governmental agencies such as the Environmental Protection Agency, Occupational Safety and Health Agency, Housing and Urban Development, and the Federal Emergency Management Agency are tasked with reducing the risk, and therefore the healthcare burden, of exposure to toxic gases, while attempting to minimize the impact on industry operations and revenues.
For example, volatile organic compounds (VOCs) are a class of widely used organic chemicals that present significant long-term and short-term health risks. These compounds have a high vapor pressure in ambient conditions and thus are readily outgassed from products that contain them. For example, VOCs are present in a wide array of products such as paints and lacquers, paint strippers, cleaning supplies, pesticides, building materials and furnishings, office equipment such as copiers and printers, correction fluids and carbonless copy paper, graphics and craft materials including glues and adhesives, permanent markers, and photographic solutions. Consequently, many people are exposed to VOCs daily.
To protect these people from dangerous exposure to hazardous environments, there is a need for inexpensive devices that measure the concentration of these harmful compounds. Existing devices for measurement of VOCs rely mainly on the photoionization detector-based technology and require high power to operate and are expensive for wide applications. The devices based on colorimetric detection of VOCs, on the other hand, are ambiguous and do not provide quantitative measurement. Therefore, there is an unmet need for a simple technology that enables development of an inexpensive sensor device for quantitative detection of VOCs for a number of applications including HazMat/Homeland Security, industrial hygiene, indoor air quality, military applications, and biomedical applications.
In addition to applications related to monitoring exposure to dangerous gas-phase chemicals and protecting the health of individuals, detection of gas-phase analytes finds uses in industrial and commercial settings. For example, some industrial applications include monitoring product performance such as interrogating vehicle emissions for release of volatile gases. Additional applications include assessing fruit ripeness and/or spoilage based on volatile gas emissions.
There is also broad potential for use of sensors of gas-phase analytes in biomedical applications. For example, sensors have been used to monitor the composition of gas mixtures used for anesthesia during surgical procedures or to monitor exhaled gases related to metabolic activities. Recently, analysis of human breath has emerged as a non-invasive technique for diagnosis of disease. The exhaled human breath contains a number of volatile gases such as oxygen, carbon dioxide, nitrogen, carbon monoxide, acetone, ammonia, hydrogen sulfide, amines, oxides of nitrogen, etc. (Manolis, 1983; Smith et al, 1999; and Diskin et al, 2003) and measurements of analytes in exhaled breath have been applied to a wide range of disease states, including diabetes (Henderson et al, 1952; Sulway et al, 1970; Crofford et al, 1977; and Novak et al, 2007), gastrointestinal disorders (Perman, 1991; Bauer et al, 2000; and Nieminen et al, 2000), and asthma (Alving et al, 1993).
While current technologies exist to measure gaseous analytes (e.g., volatile organic compounds and other compounds), these technologies do not provide timely information regarding gas levels to inform immediate actions for minimizing risks, e.g., taking appropriate measures in the medical, defense, and industrial settings to protect human health. For example, many direct-read dosimeters lack sensitivity and reproducibility and do not meet regulatory monitoring requirements. Alternatively, many indirect read technologies are shipped to an accredited laboratory for analysis, introducing a long lag-time of typically many weeks between sample collection and data retrieval. In addition, conventional technologies are also subject to substantial positive or negative interference from other pollutants and inaccuracies resulting from low air flow. There exists, therefore, an unmet need for technology that accurately measures gases and that can be read on-site to provide actionable information.
In some situations described above, it is necessary to know the concentration of the chemical environment as quickly as possible in order to minimize exposure to the chemical. In such situations a detector of the instantaneous concentration of the gas is needed. In other situations, such as but not limit to when measuring personal exposure to a vapor, it is necessary to know the cumulative exposure to the chemical that occurs of a given interval of time, such as but not limited to a workday. In this situation, a dosimeter that measures the cumulative level of exposure over a set period of time is needed.